Axial retention of permanent magnet rotor in high speed generator

ABSTRACT

A permanent magnet rotor for use on an electrical generator comprises a hub having an outer peripheral surface and an inner peripheral bore centered on an axis. The inner peripheral bore is provided with a screw thread at least over a portion of an axial dimension. Permanent magnets are mounted on the outer peripheral surface of the hub. A containment band is positioned radially outwardly of the magnets, holding the magnets and the hub together. The hub, a generator rotor incorporating the permanent magnet rotor, and a generator incorporating the permanent magnet rotor are also disclosed and claimed in this application.

BACKGROUND OF THE INVENTION

This application relates to the axial retention of a permanent magnetrotor on a generator shaft.

Electrical generators typically include a main generator winding setmounted on a rotor shaft. The main generator windings rotate inproximity to main stator windings, and generate electricity when theshaft is driven to rotate.

The operation of modern generators is quite complex, and includescontrols and safety features. A permanent magnet rotor is also fixed tothe rotor shaft, and driven to rotate adjacent to its own stator. Theenergy generated by the rotation of the permanent magnet rotor isutilized for control or safety functions. The permanent magnet rotor ispreferably precisely positioned on the rotor shaft such that it is in adesired location relative to its stator.

Typically, the permanent magnet rotor is interference fit on the rotorshaft. Under some high speed and high vibration applications, such asmay be found in an aircraft application, as an example, the permanentmagnet rotors have sometimes become loose and misaligned.

To address this, locking tabs and threaded locking nuts have beenutilized to hold the permanent magnet rotor on the rotor shaft. However,these systems have not always adequately locked the rotor itself, andfurther require additional parts, thus increasing the cost andcomplexity of assembly, as well as increasing the length and weight ofthe generator.

SUMMARY OF THE INVENTION

A hub for a permanent magnet rotor in an electrical generator includes ahub body having an outer peripheral surface and an inner peripheral borecentered on an axis. The inner peripheral bore is provided with a screwthread at least over a portion of an axial dimension from adjacent afirst end. A piloting diameter on the inner peripheral bore is largerthan a diameter to a tip of the screw thread. The piloting diameter isfor piloting on a shaft that is to receive the hub.

A permanent magnet rotor for use on an electrical generator comprises ahub having an outer peripheral surface and an inner peripheral borecentered on an axis. The inner peripheral bore is provided with a screwthread at least over a portion of an axial dimension. Permanent magnetsare mounted on the outer peripheral surface of the hub. A containmentband is positioned radially outwardly of the magnets, holding themagnets and the hub together.

A generator rotor includes a main winding mounted on a rotor shaft. Apermanent magnet rotor includes a hub having an outer peripheral surfaceand an inner peripheral cylindrical bore centered on an axis. The innerperipheral bore is provided with a screw thread at least over a portionof an axial dimension. Permanent magnets are mounted on the outerperipheral surface of the hub. A containment band is positioned radiallyoutwardly of the magnets holding the magnets and hub together. The rotorshaft has threads received on the threads on the inner peripheral bore.

A generator includes a main winding stator, and a stator for a permanentmagnet rotor. A main winding rotor is mounted on a rotor shaft. Apermanent magnet rotor includes a hub having an outer peripheral surfaceand an inner peripheral cylindrical bore centered on an axis. The innerperipheral bore is provided with a screw thread at least over a portionof an axial dimension. Permanent magnets are mounted on the outerperipheral surface of the hub. A containment band is positioned radiallyoutwardly of the magnets holding the magnets and hub together. The rotorshaft has threads received on the threads on the inner peripheral bore.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a generator.

FIG. 2 is an exploded view of a permanent magnet rotor.

FIG. 3 is an exploded view of components of the generator.

FIG. 4 is a cross-sectional view through the assembled permanent magnetrotor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A generator 20 is illustrated in FIG. 1 having a permanent magnet rotor22 fixed to a rotor shaft 23. The permanent magnet rotor 22 rotates whenthe shaft 23 is driven to rotate, and adjacent to a stator 24. Therotation of the permanent magnet rotor 22 adjacent to the stator 24generates electrical power which may be utilized for control or safetyfeatures, as known. A main winding set 26 rotates adjacent to a mainstator set 28, and generates electrical power for uses, such as for onan aircraft. One common application of the generator shown in FIG. 1 isto be driven by the gas turbine engines of a jet aircraft.

FIG. 2 is an exploded view of the permanent magnet rotor 22. As shown, acontainment band 30 surrounds a plurality of permanent magnets 32. A hub34 includes outer facets 36 which each mount a magnet 32. Due to facets36, the outer periphery of hub 34 is polygonal. An inner bore of the hub34 includes a piloting boss 38, and threads 40. As shown, a pilotingboss is at one end of the bore, and beyond threads 40.

FIG. 3 shows the permanent magnet rotor 22 assembled. As can be seen,the piloting diameter 38 faces the shaft 23, and the threads 40 are atan axial outer location. Threads 52 are formed on the shaft 23, and apiloting diameter 50 is also formed. To assemble the permanent magnetrotor 22 onto the shaft 23, the piloting diameter 38 is initially placedon the piloting diameter 50. This centers the rotor 22 properly on theshaft 23. Next, torque tool holes 54 receive a torque tool which maythen be driven to rotate the permanent magnet rotor 22 onto the shaft 23such that the threads 40 engage on the threads 52, locking and properlypositioning the permanent magnet rotor 22 on the shaft 23.

As shown in FIG. 4, when assembled, a central axis C of the shaft 23extends through the shaft 23 and the hub 34. As can be appreciated inFIG. 4, the threads 40 on the inner diameter of the hub 34 are axiallyaligned with portions of the magnets 32. Stated another way, a planecould be defined that is perpendicular to axis C, and which extends boththrough the threads 40 and through portions of the magnets 32.

As shown in FIG. 4, a first diameter D1 can be defined to a root of thethreads 52 on the shaft 23. That same diameter would be effectivelyequal to a tip of the threads 40 on the hub 34.

A second diameter D2 can be defined to the tip of the threads 52 on theshaft 23, or the root of the threads 40 on the hub 34. A third diameterD3 extends to the piloting surfaces. While there are slight differencesbetween these diameters, with regard to the diameters on the shaft 23,D1 is between 1.8730″ (47.574 mm) and 1.8798″ (47.746 mm). The diameterD2 is between 1.9294″ (49.007 mm) and 1.9375″ (49.212 mm) and thediameter D3 is between 2.0165″ (51.219 mm) and 2.0160″ (51.20 mm). Inembodiments, the ratio of D1 to D3 is between 1.07 and 1.08. This ratioholds true as to the hub, as well as the shaft.

It is preferred that the design of the threads 52 and 40 provide thatthe torque on the permanent magnet rotor 22 when it is driven in itsexpected direction during operation will serve to further tighten thepermanent magnet rotor 22 on the shaft 23, rather than being in aloosening opposed direction. In one embodiment, the screw threads were20 threads per inch. The thread utilized on the hub was a self-lockingthread available under the trade name Spiralok.

To assemble the permanent magnet rotor 32, the magnets may be sintered.The individual magnets are magnetized, tested, and stabilized. They maythen be epoxy-bonded to the facets on the hub. The hub may be made of anappropriate steel. The outer diameter of the magnets may be machined tosize. The epoxy bond is desired to keep the magnets in place during thismachining. A containment band 30 is then heated and assembled around themagnet. As the band cools, it forms an interference fit holding themagnets, hub, and containment band together. Of course, other methodsmay be used

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. A hub for being part of a permanent magnet rotor in an electricalgenerator, the hub comprising: a hub body having an outer peripheralsurface and an inner peripheral bore centered on an axis, said innerperipheral bore being provided with a screw thread over a portion of anaxial dimension from adjacent a first end; and a piloting diameter onthe inner peripheral bore being of a diameter larger than a diameter ofa tip of said screw thread, said piloting diameter for piloting on ashaft that is to receive said hub.
 2. The hub as set forth in claim 1,wherein said hub outer peripheral surface having a polygonal shape. 3.The hub as set forth in claim 1, wherein torque tool holes for receivinga torque tool to drive said hub onto a rotor shaft are included in saidhub.
 4. The hub as set forth in claim 1, wherein a ratio of saiddiameter to said piloting diameter compared to the diameter to the tipof said screw threads being between 1.07 and 1.08.
 5. A permanent magnetrotor for use on an electrical generator comprising: a hub having anouter peripheral surface and an inner peripheral bore centered on anaxis, said inner peripheral bore being provided with a screw thread atleast over a portion of an axial dimension; permanent magnets mounted onsaid outer peripheral surface of said hub; and a containment bandpositioned radially outwardly of said magnets, and holding said magnetsand said hub together.
 6. The permanent magnet rotor as set forth inclaim 5, wherein said inner peripheral bore also includes a pilotingsurface at an end beyond said threads.
 7. The permanent magnet rotor asset forth in claim 6, wherein a ratio of a diameter to said pilotingsurface compared to a diameter to an inner peripheral tip of said screwthreads being between 1.07 and 1.08.
 8. The permanent magnet rotor asset forth in claim 5, wherein a plane can be defined that isperpendicular to said axis, and said plane extends through said threadson said inner peripheral bore, and through said permanent magnets. 9.The permanent magnet rotor as set forth in claim 5, wherein said hub hastorque tool holes for receiving a torque tool to drive said permanentmagnet rotor onto a rotor shaft which will receive said permanent magnetrotor.
 10. A generator rotor comprising: a main winding rotor mounted ona rotor shaft; and a permanent magnet rotor including a hub having anouter peripheral surface and an inner peripheral cylindrical borecentered on an axis, said inner peripheral bore being provided with ascrew thread at least over a portion of an axial dimension, permanentmagnets mounted on said outer peripheral surface of said hub, acontainment band positioned radially outwardly of said magnets, andholding said magnets and said hub together, said rotor shaft havingthreads received on said threads on said inner peripheral bore.
 11. Thegenerator rotor as set forth in claim 10, wherein said inner peripheralbore of said hub includes a piloting surface at an end of said hubbeyond said threads, and said rotor shaft further being provided with amating piloting surface.
 12. The generator rotor as set forth in claim11, wherein a ratio of said diameter to said piloting surface comparedto a diameter to an inner peripheral tip of said screw threads on saidhub being between 1.07 and 1.08.
 13. The generator rotor as set forth inclaim 10, wherein a plane can be defined that is perpendicular to saidaxis, and said plane will extend through said threads on said rotorshaft, said threads on said inner peripheral bore of said rotor hub, andthrough said permanent magnets.
 14. The generator rotor as set forth inclaim 10, wherein said hub has torque tool holes for receiving a torquetool to drive said permanent magnet rotor onto said rotor shaft.
 15. Agenerator comprising: a main winding stator, and a stator for apermanent magnet rotor; a main winding rotor mounted on a rotor shaft;and a permanent magnet rotor including a hub having an outer peripheralsurface and an inner peripheral cylindrical bore centered on an axis,said inner peripheral bore being provided with a screw thread at leastover a portion of an axial dimension, permanent magnets mounted on saidouter peripheral surface of said hub, a containment band positionedradially outwardly of said magnets, and holding said magnets and saidhub together, said rotor shaft having threads received on said threadson said inner peripheral bore.
 16. The generator as set forth in claim15, wherein said inner peripheral bore of said hub includes a pilotingsurface at an end of said hub beyond said threads, and said rotor shaftfurther being provided with a mating piloting surface.
 17. The generatoras set forth in claim 16, wherein a ratio of said diameter to saidpiloting surface compared to a diameter to an inner peripheral tip ofsaid screw threads on said hub being between 1.07 and 1.08.
 18. Thegenerator as set forth in claim 15, wherein a plane can be defined thatis perpendicular to said axis, and said plane will extend through saidthreads on said rotor shaft, said threads on said inner peripheral boreof said rotor hub, and through said permanent magnets.
 19. The generatoras set forth in claim 15, wherein said hub has torque tool holes forreceiving a torque tool to drive said permanent magnet rotor onto saidrotor shaft.